Stable Isotope Profiles in Carbonate Platform Cycles: Comparison to Core-Based Cycles

Hsieh, Jean ¹; Katz, David A.¹; Harris, P. Mitch ¹; Buoniconti, Matthew ^1
1 Energy Technology Company, Chevron, San Ramon, CA.

The carbon and oxygen isotopic values of biotically and abiotically precipitated marine carbonates display significant temporal variation that is well documented through the geological record. Carbon variations have been attributed to changes in carbon cycling through changes in productivity and organic carbon burial rates, variations in carbon sources to the atmosphere and ocean, and shifts in weathering patterns and rates. Oxygen isotopic variations are attributed to secular variations in ocean chemistry, infiltration of meteoric water during exposure, and later fluid flow after burial.

The potential that the variations in marine carbonate oxygen and carbon records have as a chronostratigraphic correlation tool and paleoenvironmental proxy has also been well established over the past two decades. This study presents the results of measurements of the carbon and oxygen isotopic values for an isolated carbonate platform that ranges in age from Late Visean to Bashkirian (Carboniferous). The δ13C stratigraphy shows trends to positive and negative δ13C values that can be correlated with the major second order sequence boundaries picked using traditional facies variations based on core descriptions. At higher order frequencies, the trends are less clear and more variable with respect to facies changes. Variations are more pronounced when there are thinner cycles possibly reflecting the more frequent changes in accommodation space. With less frequent changes, e.g., thicker beds and deeper-water facies, the isotopic profiles are less variable. Several sequence boundaries could be modified and even-higher order cycle boundaries could be picked using the δ13C stratigraphy along with the oxygen data. These results suggest that stable isotope profiles can be used to help constrain the sequence stratigraphic framework of a carbonate reservoir.

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009